1. Field of the Invention
The present invention relates to a piston-cylinder unit for producing and transmitting compressive forces onto adjusting elements which are guided so as to be slidable on a straight line. The piston-cylinder unit includes a push rod which is mounted so as to be capable of oscillating transversely of the direction of the compressive forces in a unilaterally open skirt-type piston.
2. Description of the Related Art
Piston-cylinder units of the above-described type are used, particularly in heavy machine construction, for applying a controllable pressure onto plane stop surfaces from adjusting elements which are slidable in sliding guides or for counteracting in an unloading manner the pressure acting on these elements. The push rods of the piston-cylinder units act on the respective contact surface of the adjusting element without being coupled to the latter. Piston-cylinder units of this type are arranged, for example, between the chocks of rolling mill stands with one or more pairs of rolls in order to support the chocks of a pair of rolls in a pressure-controlled manner relative to each other or to apply a pressure, for example, a bending pressure, onto the ends of the rolls for obtaining a partial deformation of the rolls.
The oscillating mounting of the push rod in the skirt-type piston of the piston-cylinder units of the above-described type takes into account the fact that the adjusting elements on which the push rod acts during practical operation frequently carry out more or less substantial movements transversely of the direction of the compressive forces which are due, for example, to unavoidable tolerances in the sliding guides of the adjusting elements. When this happens, the push rod absorbs the short transverse movements without changing the pressure contact between push rod and contact surface of the adjusting element with an oscillating movement in the skirt-type piston.
In a known piston-cylinder unit of the above-described type for the application of pressure from chocks of rolling mill rolls, the push rod rests with its crowned lower end surface on a spherical indentation arranged in the bottom portion of the skirt-type piston. The possible oscillating angle of the push rod is narrowly defined by the inner wall of the skirt-type piston in which the push rod is inserted with slight play and by an annular sealing member mounted on the rim of the skirt-type piston. This is to ensure that, after the transmission of the compressive forces onto the adjusting elements have concluded, the push rod again returns into the original centered position within the skirt-type piston and is not in an inclined position when a new force application movement begins.
It has been found that this type of configuration of the piston-cylinder unit is not suitable for absorbing greater oscillating movements of the adjusting elements as they occur. For example, due to worn sliding guides of the adjusting elements as a result of continuous operation, and that even if the oscillations are only slightly increased, the annular seals are subjected to pressures which exceed the elasticity limits of the sealing members and damage the sealing members as a result.